The present invention relates to a ratchet wrench and, more particularly, to a ratchet wrench with prevention of damage to teeth of a drive member or a pawl resulting from stress concentration.
FIGS. 1-6 show a conventional reversible ratchet wrench 6 including a drive member 5 and a pawl 4. A pin 2 biased by a spring 3 presses against the pawl 4 to engage the drive member 5. A switch 1 is pivotable between two positions to change a driving direction of the ratchet wrench 6. When tightening a workpiece such as a bolt, a nut, or the like by rotating the ratchet wrench 6 in a direction, the drive member 5 also rotates in the direction. Note that the teeth of the pawl 4 meshes with the grooves of the teeth of the drive member 5. When the ratchet wrench 6 is rotated in a reverse direction, the workpiece and the drive member 5 do not rotate together with the ratchet wrench 6. This is because the force imparted from the teeth of the drive member 5 to the teeth of the pawl 4 is larger than the biasing force of the spring 3. Thus, the pawl 4 moves backward. FIGS. 4 and 5 show a momentary status of the pawl 4 in its backward movement. When the ratchet wrench 6 is further rotated in the reverse direction, the drive member 5 and the pawl 4 are engaged again as shown in FIGS. 2 and 3, for the spring 3 and the pin 2 push the pawl 4 back to its position. The workpiece can be tightened through repeated rotation of the ratchet wrench 6 in the direction and the reverse direction.
However, the engaging relationship between the drive member 5 and the pawl 4 can be adversely affected by oil therebetween. Specifically, when oil exists in upper, intermediate, and lower positions Z1, Z2, and Z3 between the drive member 5 and the pawl 4, the pawl 4 inclines and, thus, can not completely mesh with the drive member 5. Thus, the teeth of the pawl 4 partially engage with the teeth of the drive member 5, and thus, have a smaller engaging area with the teeth of the drive member 5 when the ratchet wrench 6 is rotated in the direction. Stress concentration occurs, leading to damage to the teeth of the drive member 5 or the pawl 4 or even to injury to the user. Stress concentration may also occur when the ratchet wrench 6 has normal tolerances in verticality and parallelism of the compartments, grooves, and holes receiving the drive member 5, the pawl 4, and the switch 1. Although stress concentration can be reduced by high-precision processing, the costs are high and the yield is low.
Thus, a need exists for a ratchet wrench that can prevent damage to the teeth of the drive member or the pawl resulting from stress concentration without high-precision processing.